This invention relates to improvement in an oxygen absorbent comprising iron and a metal halide.
In order to preserve foodstuffs, such as vegetables, fish, shellfish, meats, processed foodstuffs, such as potato chips, cakes, peanuts, etc., and so on, it is necessary to prevent the foodstuffs from getting moldy and from putrefying. Prior art methods have used freezer storage, cold storage, vacuum packaging and replacing the gas present in the inner part of packaging by an inert gas to prevent foodstuffs from getting moldy and putrefying. Additives, such as antioxidants, have been used for preserving foodstuffs. Recently, governments have started to regulate the use of additives in food, since it is realized that some additives are injurious to humans. The freezer storage method, requiring large-scale apparatus and complicated operation, is costly.
Molds or eumycetes, bacteria and higher organisms, such as insects, tend to disturb preservation of foodstuffs. These molds, eumycetes, bacteria and insects live and grow in the presence of oxygen and cause putrefaction and change in quality of foodstuffs.
Therefore, if oxygen can be selectively removed from the atmosphere in which the foodstuffs are packed, the problem of putrefaction and change in quality of foodstuff can be overcome, and it will become possible to preserve foodstuffs for a long time.
Attempts have been made for producing such an oxygen absorbent.
Japanese Patent Publication No. 19729/1972 discloses the use of an oxygen absorbent comprising hydrosulfite, calcium hydroxide, sodium bicarbonate, activated carbon and optionally water to preserve vegetables by removing oxygen from atmosphere.
U.S. Pat. No. 2,825,651 proposes a process for preparing an oxygen absorbent comprising mixing a finely divided sulfite and a finely divided metal salt, at least one of the two compounds having water of hydration or crystallization and compression-pelletizing the mixture in order to increase the rate of the oxidation of the sulfite.
British Pat. No. 553,991 discloses the steps of forming pilules comprising carbon and highly activated iron powder obtained by hydrogen treatment, followed by absorbing oxygen in a hood using the resulting pilules. Since iron powder contained in the pilules is highly active, the iron intensely reacts with oxygen in the container to remove oxygen therein. Since there is the possibility of fire when using such highly active iron powder, the process of British Pat. No. 553,991 is dangerous.
The present inventors have carried out wide research to find an oxygen absorbent not having such disadvantages. As a result, it was found that a metal powder alone has a slow oxidizing rate in air and is therefore not usable as an oxygen absorbent for preventing putrefaction of foodstuffs and change in quality of foodstuffs, and that even when the metal powder is mixed with water, the oxidizing rate thereof does not increase.
It was found that the mixture of a metal powder, a metal halide and water has rapid oxidizing rate. U.S. Ser. No. 816,134 filed on July 15, 1977 now U.S. Pat. No. 4,127,503 assigned to the assignee of this application discloses comprizing a metal powder and a metal halide coated thereon. However, it was found that though such oxygen absorbent comprising a metal powder and a metal halide has satisfactory oxygen-absorbing ability, evolution of small amount of hydrogen occurs during storage of the absorbent or when oxygen is absorbed. When a large amount of an oxygen absorbent is used in a closed container, this is dangerous, because there is possibility of evolution of hydrogen to the point of explosion.